Hi everyone
I have a quick question for anyone that has built a valve amp from scratch. I want to build the project featured in this link.
OddWatt Audio 5751 SRPP / KT88 Push-Pull Monoblock Tube Amplifier Kits
I think most of you have probably seen this amp as a project in one form or another. I live in South Africa and shipping is prohibitive on items like output transformers and the chassis. I got the transformers custom wound here and thought I might build the case in wood instead of attempting to work sheet aluminium. I see many of these types of amps use the case as a ground plane so I was wondering what changes / precautions I should take if I make a wood case?
Do the transformer casings need to be grounded as they would be if bolted to a metal chassis?
Are there some reasons to avoid wood like EMI interference / hum?
Thanks for any help.
I have a quick question for anyone that has built a valve amp from scratch. I want to build the project featured in this link.
OddWatt Audio 5751 SRPP / KT88 Push-Pull Monoblock Tube Amplifier Kits
I think most of you have probably seen this amp as a project in one form or another. I live in South Africa and shipping is prohibitive on items like output transformers and the chassis. I got the transformers custom wound here and thought I might build the case in wood instead of attempting to work sheet aluminium. I see many of these types of amps use the case as a ground plane so I was wondering what changes / precautions I should take if I make a wood case?
Do the transformer casings need to be grounded as they would be if bolted to a metal chassis?
Are there some reasons to avoid wood like EMI interference / hum?
Thanks for any help.
If you don't like metal work, I suggest building a wood frame and attaching a sheet metal top plate to it. I think with an all-wood enclosure, you'll have issues with material thickness that interferes with tube sockets and the like. Drilling a couple of holes in a sheet of aluminum is really quite easy and you can use most of your wood tools for this anyway.
The insides should be covered in metal. I'd use thin metal screen like the stuff used for decorations and such. You can generally find copper or brass screen material in arts & crafts stores. I've also found some galvanized steel screen used for vents and such at my local building hardware store. That would work as well. The screen should be grounded.
All metal parts that can be couched by the user should be grounded as well.
~Tom
The insides should be covered in metal. I'd use thin metal screen like the stuff used for decorations and such. You can generally find copper or brass screen material in arts & crafts stores. I've also found some galvanized steel screen used for vents and such at my local building hardware store. That would work as well. The screen should be grounded.
All metal parts that can be couched by the user should be grounded as well.
~Tom
Back in the olden days of tube radio most of them came in a wooden case. Better screening from electrical interferences is achieved with a metal case and this is an important consideration with pre-amps and tuning circuits where low level signals are involved but not as much of a problem with power amplifier amplifiers. Still - anything you can do to minimize interference is always desirable.
Here is a link to something similar to what you are considering and there are many more examples available on the 'Net - do your research and look around.
DIY 6T9 Push-Pull Tube Amplifier Project
DIY 6T9 Tube (Valve) Single-Ended Amplifier Kit
Here is a link to something similar to what you are considering and there are many more examples available on the 'Net - do your research and look around.
DIY 6T9 Push-Pull Tube Amplifier Project
DIY 6T9 Tube (Valve) Single-Ended Amplifier Kit
Hi just for interest..
Post 3848 and 3851 in this thread:
http://www.diyaudio.com/forums/tubes-valves/71300-photo-gallery-385.html
The main thing is make sure the top and case can carry the weight of the Transformers...You can put circuit board under the top to give screening and grounding..if you use it as a ground plane then use a tool to engrave slits in the copper coating between any components so you don't have any conduction arround holes for valve bases...make sure if you take a supply cable through a hole in it bring the return supply cable through the same hole (eddy currents)..Yes Tx chassis must be earthed..
Regards
M. Gregg
Post 3848 and 3851 in this thread:
http://www.diyaudio.com/forums/tubes-valves/71300-photo-gallery-385.html
The main thing is make sure the top and case can carry the weight of the Transformers...You can put circuit board under the top to give screening and grounding..if you use it as a ground plane then use a tool to engrave slits in the copper coating between any components so you don't have any conduction arround holes for valve bases...make sure if you take a supply cable through a hole in it bring the return supply cable through the same hole (eddy currents)..Yes Tx chassis must be earthed..
Regards
M. Gregg
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My first ever amp was all wooden chassis. Dead quiet.
Recommended. RF rarely is a problem. I would not bother with shielding at all.
Amps made with a wooden frame with an aluminium or copper top plate are very common and have no problems either with shielding. Even if you have an all metal enclosure. That is still no guarantee that it is shielded properly.
Go for it. With regards to safety you should have all exposed metal parts such as transformers connected to your ground.
Recommended. RF rarely is a problem. I would not bother with shielding at all.
Amps made with a wooden frame with an aluminium or copper top plate are very common and have no problems either with shielding. Even if you have an all metal enclosure. That is still no guarantee that it is shielded properly.
Go for it. With regards to safety you should have all exposed metal parts such as transformers connected to your ground.
Attachments
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Ok,
Where is the underside shot..its always the most interesting..well I think so anyway..
I like wood its better than a sterile chassis....Birds eye maple would be nice....I think I even prefer it to a metal top plate....and I hate shellac but I keep touching it and cant stop looking at it.....LOL Shellac dosen't like heat either but who cares...I would use it again its just such a pain ....I can agree that this is one of the quietest I have made dead silent..
Regards
M. Gregg
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I see,
you have screened the caps..I do that as well..it works great, even with aluminium foil and drain wire..wrap with tape and varnish. or copper foil and solder.
This getting me thinking again...
The OP tubes have to be isolated from the wooden top plate..I recessed them in and mounted on silicone washers..also the Transformers to reduce any vibration. I guess you could just distance them using fixed sockets..(The type that the mounting ring is fixed to the socket/base).
I used long thread "red copper" speaker jacks..compared to my silver plated ones they are much better.. Also the input phonos can be mounted on a drilled copper plated PCB board and Gnd to board and isolate the Jacks from the board so they have a seperate star Gnd. with PCB shield...it makes it easier to mount in a square cut out..spray the board black works well..drill some glass for the front panel or use tiles.. mount the volume etc on PCB again behind the tile or glass and ground the copper on the board..(creates a shield) don't etch it just use it as a mounting material as though it was copper sheet..screw it (inside) to the wooden chassis then you can remove it to replace the volume if you need to without removing the glass front plate. No screws showing.
Regards
M. Gregg
you have screened the caps..I do that as well..it works great, even with aluminium foil and drain wire..wrap with tape and varnish. or copper foil and solder.
This getting me thinking again...
The OP tubes have to be isolated from the wooden top plate..I recessed them in and mounted on silicone washers..also the Transformers to reduce any vibration. I guess you could just distance them using fixed sockets..(The type that the mounting ring is fixed to the socket/base).
I used long thread "red copper" speaker jacks..compared to my silver plated ones they are much better.. Also the input phonos can be mounted on a drilled copper plated PCB board and Gnd to board and isolate the Jacks from the board so they have a seperate star Gnd. with PCB shield...it makes it easier to mount in a square cut out..spray the board black works well..drill some glass for the front panel or use tiles.. mount the volume etc on PCB again behind the tile or glass and ground the copper on the board..(creates a shield) don't etch it just use it as a mounting material as though it was copper sheet..screw it (inside) to the wooden chassis then you can remove it to replace the volume if you need to without removing the glass front plate. No screws showing.
Regards
M. Gregg
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Thanks for the tips guys. This is making me very keen to get started. Damn this research paper!
Just a question, how is the cap isolation done? Do you wrap the cap in some copper/aluminium foil and then ground that on a star ground point? Why is this done?
I like the all wood look but if I do go for a brass plate it might be fun to make it into a steampunk valve amp.
Thanks again for the help.
@Bas. I am glad you liked South Africa, its difficult to convince people to come out here sometimes. Did you come here for the World Cup and which places did you visit?
Just a question, how is the cap isolation done? Do you wrap the cap in some copper/aluminium foil and then ground that on a star ground point? Why is this done?
I like the all wood look but if I do go for a brass plate it might be fun to make it into a steampunk valve amp.
Thanks again for the help.
@Bas. I am glad you liked South Africa, its difficult to convince people to come out here sometimes. Did you come here for the World Cup and which places did you visit?
You wrap tape around the cap. And connect a drain wire to the part with the lowest potential i.e. to ground.
Sorta like shielding. I did it because I wanted to do it.
Theoretically you want the outer shield of the cap to perform that function. When I say outer shield I mean the part of the capacitor that is most on the outside. And it can lead to a measurable improvement...in the performance of the cap itself.
But I never figured out how to do that. So I thought...I'll just do it this way. But I haven't since because of the price of copper tape.
Sorta like shielding. I did it because I wanted to do it.
Theoretically you want the outer shield of the cap to perform that function. When I say outer shield I mean the part of the capacitor that is most on the outside. And it can lead to a measurable improvement...in the performance of the cap itself.
But I never figured out how to do that. So I thought...I'll just do it this way. But I haven't since because of the price of copper tape.
That is an awesome looking box. I definitely couldn't make that in 1 evening but I agree the wood direction is easier and I think looks much better than the standard black aluminium box. I also would like to learn some Neapolitan intaglio techniques to make seriously beautiful boxes. Something like this.
Buy.com - Sorrento Italian-Style Round Inlaid-Wood Serving Cart
Or this
"Sorrento Inlaid Wood Box" - Photo of Sorrento, Italy by KristenBentz - IgoUgo
Unfortunately I am nowhere near that skill level. I have to start somewhere.
Buy.com - Sorrento Italian-Style Round Inlaid-Wood Serving Cart
Or this
"Sorrento Inlaid Wood Box" - Photo of Sorrento, Italy by KristenBentz - IgoUgo
Unfortunately I am nowhere near that skill level. I have to start somewhere.
@Bas Its awesome to hear from another RSA guy out there.
I struggle to find parts here, especially nice caps and sometimes valves. I don't suppose you might know of any decent suppliers. Most electronic shops have the basic usual stuff, but I cant find say Mundorf or Clarity Cap suppliers. For now I am buying overseas and getting it shipped.
I struggle to find parts here, especially nice caps and sometimes valves. I don't suppose you might know of any decent suppliers. Most electronic shops have the basic usual stuff, but I cant find say Mundorf or Clarity Cap suppliers. For now I am buying overseas and getting it shipped.
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